In patients with the hypereosinophilic syndrome, 2-D echocardiography is useful in identifying the probable etiology of 2 important cardiac manifestations. Thickening of the posterobasal wall is usually associated with impairment of posterior mitral leaflet function, resulting in mitral regurgitation. Because the hypereosinophilic syndrome is associated with the peripheral embolization, thrombus formation and subsequent endocardial scarring, the noninvasive identification of intracavitary ventricular thrombi is of potential importance.